Q: I am a woman in my late 40s and I recently had an ultrasound scan of my left knee. The report showed that there is 'lobulated cystic well encapsulated lesion containing internal debris within the postero-medial aspect of the left knee... Sonographic appearances are in keeping with a Ber's cyst. There is no internal vascularity or calcification. The lesion measures about 3.7 x 2.5 x 4cm'.

What is all this in layman's terms? Do I need surgery or are there other options available? I am very reluctant to have surgery for fear of post-surgery complications.

A: The ultrasound description is typical of a Baker's cyst (sometimes also called a popliteal cyst). This is a benign, fluid-filled lesion commonly associated with underlying osteoarthritis or cartilage injury of the knee. It is usually located at the back of the knee on the medial aspect (inside). The cyst itself usually does not cause symptoms unless it is very large or if it ruptures but the latter is uncommon.

Most of the time, the cyst can be left alone as it is asymptomatic. However, the underlying osteoarthritis or cartilage injury of the knee will need to be treated. If the cyst is very large and causes discomfort, it can be aspirated (have its fluid removed) and corticosteroid can be injected. Surgical excision for this condition is rarely necessary.- Dr Kevin Lee

This article was first published in Mind Your Body, The Straits Times.